Weak continuous measurements of multiqubits systems

Weak continuous measurements of multiqubits systems In this review we summarize our recent experiments on the investigation on superconducting qubits. Instead of strong projective measurement used by other groups in their first pioneering experiments we have proposed and realized a weak continuous readout which belongs to the class of quantum non-demolition measurements. Moreover, our scheme enables to measure a superconducting qubit at the so called sweet (or magic) point where a qubit is in a superposition of two classical states and its sensitivity to external noise is minimized. In this scheme, which is widely used nowadays, the superconducting oscillator coupled to superconducting qubit is used as a detector of the qubit’s state. Such system is analogue to a system of a single atom interacting with photons in a cavity, which allows to study quantum electrodynamics in artificial macroscopic systems. Pushing this analogy we demonstrate Sisyphus cooling and amplification caused by energy exchange between an oscillator and a flux qubit. Using the Sisyphus effect we show consistency between the adiabatic weak continuous measurement in the ground state and the spectroscopic measurement. This allows us to characterize the more complicated system of coupled qubits by making use of the same method. We have realized and studied fixed ferromagnetic, antiferromagnetic as well as tunable qubit–qubit coupling. We argue that ground state measurements can be used for characterization of entangled states in coupled flux qubits. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Quantum Information Processing Springer Journals

Weak continuous measurements of multiqubits systems

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Publisher
Springer Journals
Copyright
Copyright © 2009 by Springer Science+Business Media, LLC
Subject
Physics; Quantum Information Technology, Spintronics; Quantum Computing; Data Structures, Cryptology and Information Theory; Quantum Physics; Mathematical Physics
ISSN
1570-0755
eISSN
1573-1332
D.O.I.
10.1007/s11128-009-0096-y
Publisher site
See Article on Publisher Site

Abstract

In this review we summarize our recent experiments on the investigation on superconducting qubits. Instead of strong projective measurement used by other groups in their first pioneering experiments we have proposed and realized a weak continuous readout which belongs to the class of quantum non-demolition measurements. Moreover, our scheme enables to measure a superconducting qubit at the so called sweet (or magic) point where a qubit is in a superposition of two classical states and its sensitivity to external noise is minimized. In this scheme, which is widely used nowadays, the superconducting oscillator coupled to superconducting qubit is used as a detector of the qubit’s state. Such system is analogue to a system of a single atom interacting with photons in a cavity, which allows to study quantum electrodynamics in artificial macroscopic systems. Pushing this analogy we demonstrate Sisyphus cooling and amplification caused by energy exchange between an oscillator and a flux qubit. Using the Sisyphus effect we show consistency between the adiabatic weak continuous measurement in the ground state and the spectroscopic measurement. This allows us to characterize the more complicated system of coupled qubits by making use of the same method. We have realized and studied fixed ferromagnetic, antiferromagnetic as well as tunable qubit–qubit coupling. We argue that ground state measurements can be used for characterization of entangled states in coupled flux qubits.

Journal

Quantum Information ProcessingSpringer Journals

Published: Feb 18, 2009

References

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